A piece only becomes a jewel during finishing
Casting delivers the raw metal in the shape of the jewelry. But it is the surface treatment that transforms that rough, dull, and irregular piece into a polished, shiny jewel with high perceived value. Finishing accounts for up to 40% of the final value of a piece of jewelry — which is why it deserves as much technical attention as design and casting.
In this article, MS Soluções para Joalheria explains the three main surface treatment techniques — mechanical polishing, electropolishing, and electroplating — using technical and practical language for industry professionals.
Mechanical polishing: the foundation of every finish
What it is
Mechanical polishing is the process of progressively removing surface irregularities from the metal using abrasives of decreasing grain size — from coarsest (which removes burrs and casting marks) to finest (which provides a mirror finish).
Abrasives in the correct sequence
1. Sandpaper (100 to 400 grit): removes coarse burrs, injection marks, and larger casting irregularities. Use wet sandpaper in unidirectional movements to avoid circular scratches. 2. Abrasive sponge (600 to 1000 grit): eliminates scratches from the previous sandpaper. Essential for curved geometries where flat sandpaper cannot reach. 3. Green abrasive paste (pre-polishing): used with a bench motor and felt or sisal disc. Reduces micro-scratches and prepares the surface for the final shine. 4. White or rouge abrasive paste (final polish): used with a soft cloth disc. Provides the definitive mirror shine. 5. Tumble polishing (optional for series): for mass production, the tumbler with ceramic or plastic abrasives automatically pre-polishes dozens of pieces simultaneously — saving hours of bench work.
Common polishing errors
Skipping steps to save time — the result is a surface with visible scratches under bright light. Using rouge paste without pre-polishing — the shine becomes superficial and fades quickly. Over-polishing areas with intentional texture — this destroys details that were aesthetic design differentiators.
Electropolishing: perfect shine where mechanical tools cannot reach
What it is
Electropolishing is an electrochemical process that removes a uniform, micrometric layer of the metal surface using an acid solution and electric current. The piece is connected to the positive pole (anode), and dissolution occurs preferentially on micro-protrusions — resulting in a surface smoother and brighter than mechanical polishing could produce.
What it is used for
Ideal for: interiors of rings and surfaces difficult to reach mechanically; pieces with organic or intricate textures where mechanical polishing would destroy the details; pre-plating finish on silver pieces (removes the oxide layer for better bath adhesion); internal surfaces of clasps and hinges.
Limitations
Electropolishing removes metal — very thin pieces may lose critical thickness if the process is excessive. It does not replace polishing on pieces with coarse casting defects — it amplifies defects rather than hiding them. Requires PPE and careful handling of acidic solutions.
Electroplating: color, protection, and value
What it is
Electroplating is the process of electrolytically depositing a layer of metal onto the jewelry surface. The most used in jewelry are: Rhodium plating (over silver or white gold): exceptional hardness, bright white, resistance to yellowing; Yellow, rose, or white gold plating (over silver or base metals): gives the appearance of solid gold at a much lower cost; Ruthenium plating: matte or shiny black finish for contemporary jewelry; Copper plating: used industrially as an adhesion sub-layer before nickel or gold.
Plating thickness and durability
The thickness of the galvanic deposit is measured in microns (µm). For daily-use jewelry: minimum of 0.5µm of rhodium for good durability. For high-end jewelry: 1µm to 2µm for prolonged durability. Very thin plating (below 0.3µm) wears out in weeks on daily-use pieces — and is frequently the cause of customer complaints about jewelry 'losing its color'.
Prerequisites for a quality bath
Electroplating does not forgive poorly prepared surfaces. The mandatory sequence before the bath: correct polishing; chemical degreasing (degreaser specific for precious metals); acid activation (removes surface oxide); rinse in deionized water; immediate galvanic bath — exposure to air between activation and the bath generates a new oxide layer that compromises adhesion.
When to use each technique — practical summary
Mechanical polishing: always, as a mandatory base for any subsequent finish. Electropolishing: when there are internal surfaces, delicate textures, or as pre-treatment before electroplating. Electroplating: when you want to change the color, increase surface durability, or raise the perceived value of the piece.
Conclusion: the finish is your jewelry brand's business card
A poorly finished jewel, no matter how beautiful the design, does not sell — or sells at a discount. A well-finished jewel, even with a simple design, conveys quality and justifies a premium price. Invest in the right finishing techniques and see the difference in the value perceived by the customer.
MS Soluções para Joalheria offers complete technical guidance on finishing and can recommend the best suppliers of equipment and products for each stage. Get in touch and speak with our experts.
See also: 7 mistakes that ruin molds and casting | How to organize the workflow in your jewelry studio
Want to learn the entire modern jewelry process in practice? Check out our Complete Professional Casting and Molding Course or follow us on Instagram @ms.solucoesparajoalheria.
